The present invention relates generally to an attachment mechanism for mounting a cooling device to a component to be cooled. More specifically, the present invention relates to an attachment mechanism including a plate with a hinge and a pivotally mounted latch assembly for connecting a cooling device carried by the plate with a component to be cooled.
It is well known in the electronics art to place a heat sink in contact with an electronic device so that waste heat generated by operation of the electronic device is thermally transferred into the heat sink thereby cooling the electronic device. With the advent of high clock speed electronic devices such as microprocessors (xcexcP), digital signal processors (DSP), and application specific integrated circuits (ASIC), the amount of waste heat generated by those devices and the operating temperature of those devices are directly proportional to clock speed. Therefore, higher clock speeds result in increased waste heat generation which in turn increases the operating temperature of the device. However, efficient operation of the device requires that waste heat be effectively removed.
Heat sink devices came into common use as a preferred means for dissipating waste heat from electronic devices such as the types described above. In a typical application, a component to be cooled is carried by a connector that is mounted on a PC board. Efficient dissipation of heat from the component by the heat sink depends to a large extent on the thermal contact between the heat sink and the component and the contact pressure between the heat sink and the component. Ideally, an attachment device, such as a clip, positions the heat sink so that the a surface of the heat sink that is in contact with the component is substantially flat and the contact pressure between the heat sink and component acts along a load axis that is centered on the component.
There are, however, several disadvantages to prior clips for mounting a heat sink to a component. First, many of the prior clips are manufactured from a raw material such as spring steel or Stainless Steel, for example. The raw material that is ultimately selected must be of a punch and formable grade. Consequently, a spring rate of the material selected must be low and the hardness of the material must also be low so that a punch step and a forming step that are used to manufacture the clip can successfully punch and form the material into a clip. If the spring rate and hardness of the material are too high, then the material will be extremely difficult to punch and form. Additionally, a lifetime of a die that is used to punch and form the material will be reduced.
Second, the aforementioned spring rate of the material selected for the clip does not remain constant throughout the manufacturing process. Several factors contribute to variations in the spring rate including: variations in raw material sizing; variations in post process steps; and differences in elemental compounds that are used to form alloys of the material used for the clip. Because the objective of using a clip is to apply a load on the heat sink and the component such that heat is efficiently transferred from the component to the heat sink. As a result of the aforementioned variations, there are variations in a load characteristic of clips produced from different batches of raw materials and/or by different processing steps.
Third, another property of the clip that is directly related to the spring rate is a spring back property. If a clip is made from a material with a high spring back property, then it is more difficult to form and achieve a required profile in the clip as the tools used for forming those profiles require a substantial amount of spring back compensation. Another consequence of the high spring back property is that it makes it difficult to achieve a desired dimensional accuracy in the clip.
Fourth, a load center of the clip depends on accurate dimensions for each arm of the clip. However, due to the above mentioned spring back property, there will be variations in the arm lengths that result in the load center being offset from an ideal position. Consequently, the load center will not act on the required point with a resulting increase in a contact resistance between the heat sink and the component. The higher the contact resistance results in less efficient heat removal of waste heat from the component by the heat sink.
Fifth, to compensate for the spring back property associated with the material selected for the clip, in some cases, a soft material is selected for the forming process. After forming, the soft material is heat treated to harden the material. However, the material deforms during the heat treatment process and causes the load center to shift with the same results as described above.
Sixth, another disadvantage of prior clips is that they are difficult to install and difficult to remove. For instance, to install a prior clip, a latch portion on an arm of the clip must be tilted during insertion followed by pushing the latch portion back to attach the latch portion to a tab or the like on the connector that carries the component. On the other hand, to remove the prior clip, a special tool is usually required to tilt a handle on the clip so that the latch portion disengages from the connector. In some cases, the handle is so small that it is not easy to remove the clip using the special tool and is extremely difficult if not impossible to remove the clip by hand.
Finally, a typical prior clip that is made from a material such as sheet metal, for example, is designed to exert a total load force of about 25 lbs. To exert a higher load force requires either the thickness of the material be increased or the hardness of the material be increased to achieve a higher spring rate that will result in a higher load force. However, increasing the thickness and/or the spring rate of the material makes the material extremely difficult to punch and form and also reduces die life.
Consequently, there is a need for an attachment device that is made from a material that eliminates the aforementioned dependence on spring rate and material hardness, eliminates variations in spring rate due to variations in material properties or variations in processes used to form the material, and that eliminates variations in load characteristics. There exists a need for an attachment device that eliminates dependance on a materials spring back property and the resulting difficulties in manufacturing clip profiles that arise from the spring back property. Additionally, there is also a need for an attachment device that provides for an accurate load center that is free from offset due to the aforementioned variations in the spring back property caused by arm length variations and/or heat treating a soft material. There is a need for an attachment device that is capable of exerting a high total load force without increasing material thickness or material hardness to achieve a higher spring rate commensurate with the high total load force and that achieves the high total load force without reducing die life. Finally, there is a need for an attachment device that is easy to install and remove without the need for special tools and that can be installed or removed by hand.
The attachment mechanism of the present invention solves the aforementioned problems. The problem associated with the use of punch and formable materials such as steel or Stainless Steel with a low spring rate and a low hardness are solved by using a plate. The plate can be made from a rigid material, such as a metal, for example. The plate can be formed by die casting, injection molding, and stamping, for example.
Furthermore, the problems associated with variations in spring rate and the resulting variations in the load characteristics of the prior spring clips are eliminated by using a rigid material for the plate thereby providing for a consistent load characteristic. The plate is substantially immune to variations in spring rate caused by processing steps applied to the plate during its manufacture. Moreover, the use a latch assembly including a spring for exerting a load force provides for a consistent load force between the cooling device and the component. The load force can be tailored based on spring size and the load force can be selected to easily exceed the 25.0 lbs limit of the prior spring clips.
The attachment mechanism of the present invention also solves the problems associated with the spring back property of prior clips because the use of the plate and the latch assembly eliminates the need to form clip profiles, to achieve dimensional accuracy in those clip profiles, and to provide for spring back compensation in tools used to form the clip profiles. Additionally, the shifting of the load center of prior clips caused by inaccurate spring profiles is also eliminated by using the plate.
The plate solves the problems associated with a load center shift caused by heat treating a prior spring clip made from a soft material. The use of a spring in the latch assembly solves the problems associate with using a thicker material with a higher spring rate to achieve a high load force.
Finally, the difficulties associated with installation and removal of prior clips are solved by the attachment mechanism of the present invention through the use of a hinge and a pivotally mounted latch assembly that allow the attachment mechanism to be installed and removed by hand, and without the need to use special tools to effectuate installation and removal.
Broadly, the present invention is embodied in an attachment mechanism for connecting a cooling device, such as a heat sink or the like, with a component to be cooled. The component is carried by a connector and the attachment mechanism includes a hinge and a pivotally mounted latch assembly that are adapted to be removably connected with the connector.
The attachment mechanism includes a plate having opposed mounting and base surfaces, a bore, a hinge slot, and a latch slot. The bore, the hinge slot, and the latch slot extend through the mounting and base surfaces. The bore is adapted to connect with the cooling device. The attachment mechanism also includes a hinge and a latch assembly that are adapted to be inserted into the hinge slot and the latch slot respectively.
The hinge includes a flange that prevents complete insertion of the hinge into the hinge slot and a hinge portion having an aperture therein. The aperture is adapted to be removably hinged with the connector.
The latch assembly includes a handle portion having a slot therein, a keeper positioned in the slot, a plurality of tilt relief profiles, and a latch portion having a latch profile that is adapted to be removably latched with the connector, a retention aperture formed in the latch portion, and a stop adapted to be inserted into the retention aperture. A spring locator is movably positioned in the slot. The spring locator includes a spring guide extending outward of a spring face and a slot guide extending outward of a slot face, and a spring connected with the keeper and the spring guide and operative to exert a load force between the cooling device and the component.
The latch assembly is positioned in the latch slot with the retention aperture of the latch portion positioned below the base surface, the slot guide positioned in the latch slot, and the slot face in contact with the mounting surface. Because the spring guide is movable in the slot, insertion of the latch assembly urges the keeper towards the spring guide and compresses the spring. The stop is positioned in the retention aperture to maintain the spring in compression and to prevent the latch assembly from being pulled out of the latch slot by a force exerted by the compressed spring such that the latch assembly is retained in the latch slot.
The latch assembly is urged downward into the latch slot to align the tilt relief profiles with the mounting surface and the base surface so that an actuation force applied to the handle portion radially tilts the latch assembly (i.e. radially pivots) within the latch slot to latch and unlatch the latch profile with the connector.
In one embodiment of the present invention, the handle portion of the latch assembly includes a handle that is adapted to be gripped by a hand so that the latch assembly can be easily actuated to latch or unlatch the latch profile from the connector.
In another embodiment of the present invention, the flange on the hinge is in contact with the mounting surface and straddles the hinge slot to prevent complete insertion of the hinge into the hinge slot.
In one embodiment of the present invention, the aperture of the hinge portion includes an aperture profile selected to match a complementary profile on the connector. Similarly, in another embodiment of the present invention, the latch profile is selected to match a complementary profile on the connector.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.